Why is there no lazy `format`?

[burt]

Hello,

I noticed that there is the function `formattedWrite`, which 
outputs its resulting strings to an output range, as follows:
```
unittest
{
     auto output = appender!string();
     output.formattedWrite!"%s %s"(1, 2);
     assert(output.data == "1 2");
}
```

But why is there no formatting function that returns a lazy input 
range? That way, string formatting with (barely) any allocation 
would be possible, in the following way:
```
@nogc unittest
{
     auto range = formatRange!"%s %s"(42, 43);
     assert(range.front == "42");
     range.popFront();
     assert(range.front == " ");
     range.popFront();
     assert(range.front == "43");
     range.popFront();
     assert(range.empty);
}
```

The range returned by `formatRange` could have an internal buffer 
of maybe 16 characters that stores small strings, e.g. for small 
integers. It would also allow chaining with other range 
algorithms: you would call `.joiner()` on it to get an input 
range of chars.

Is this something worth including in the standard library 
(presumably in std.format)?

(The same may also be possible for `std.conv.text` but I did not 
look into this.)